This invention relates to glass halogen lamps and, in particular, to subminiature glass halogen lamps having a ceramic base.
In the prior art, the discovery of what is now known as the halogen cycle has substantially reduced the problem of bulb blackening due to evaporation of tungsten from the incandescent filament during the life of the lamp. While a variety of lamps have been introduced incorporating this discovery, producing different size lamps is not merely a matter of scale, i.e., changing the size of the envelope and filament. A lower limit on the size of the lamp was reached due to the need for metal foil in the seal interconnecting the inner and outer leads of the lamp. The foil was necessary because of the difference in temperature coefficient of expansion between the foil, usually comprising molybdenum, and the quartz envelope.
This problem was solved with the glass halogen lamp wherein the tungsten or molybdenum lead wires are brought directly through the seal without the use of a foil interconnection. Since the broad foil segments are obviated, the width of the seal becomes compatible with subminiature lamp sizes, i.e., lamps having an envelope diameter of 0.64 cm. (0.25 inches) or less. A more complete description of this lamp and its advantages is contained in U.S. Pat. No. 3,798,491.
While commercially well received, the use of the lamp has been somewhat restricted due to the difficulty some potential users have in handling the fine 2.5.times.10.sup.-2 cm. (10 mil) molybdenum leads from the lamp. Welding the leads results in an undesirable, permanent connection. Soldering to molybdenum is rather difficult. In the past, the difficulty of electrically connecting the lamp to a power source was overcome by providing a two-pin ceramic base for the lamp, which had the added benefit of enabling the finished lamp to be prefocused. In this assembly, tubular pins are staked to a ceramic base shell. The wire lamp leads are inserted into the tubular pins and connected using a combination crimp-weld.
The pin staking operation limits the size of the base shell and pin space and is costly. The crimp-weld operation deforms the pins and often results in unsatisfactory electrical contact. In addition, pin length is restricted to the length of the pin being staked, requiring extensive inventories of bases for different lamp types.